1. Field of the Invention
The present invention relates to a vehicle which can turn with a smaller turning radius.
2. Description of the Related Background Art
For four-wheel vehicles, a parameter called the xe2x80x9cturning radiusxe2x80x9d is known for indicating the performance of each four-wheel vehicle. A vehicle having a smaller turning radius can make a smaller turn at a corner during a turning operation such as U-turn.
Vehicles employing four-wheel steering (4WS) have been known as prior art four-wheel vehicles which can improve the turning radius. The 4WS refers to a system which controls the steering angle (rudder angle) of not only front wheels but also rear wheels in association with a manipulation through a steering wheel. The 4WS system can reduce the turning radius due to the controllable steering angle provided to the rear wheels.
A fifth wheel system is also known as an improvement in the turning radius. The fifth wheel system additionally has a fifth wheel stored below the floor, in addition to four wheels, such that the fifth wheel is slightly protruded relative to the other wheels during a turn to lift up the vehicle body, and the fifth wheel is driven to have the vehicle make a turn.
However, the 4WS, while it is effective in reducing the turning radius, suffers from limitations to the reduction in the turning radius since the steering angle is limited in order to suppress an inherent shake-out phenomenon to a practically ignorable extent. The fifth wheel system in turn is expected to provide significant effects, but implies problems that the vehicle becomes unstable due to a three-wheel state during a turning operation, the mechanism involved in the system tends to be complicated, and a large space is required to accommodate the mechanism including the fifth wheel.
It is therefore an object of the present invention to provide a vehicle which is capable of turning with a relatively simple turning mechanism, which saves a required space, to sufficiently reduce the turning radius.
A four-wheel vehicle equipped with turning mechanism according to the present invention comprises a rotatably supporting device for supporting one of front and rear pairs of left and right wheels, to which running torque produced by a driving force is not transmitted, for rotation concerning respective axes perpendicular to the ground; a rotating position fixing device for fixing the one pair of left and right wheels at respective angular positions along tangential directions of an arc passing the axes perpendicular to the ground of the one pair of left and right wheels, and having the center located near a center point of a rotating axle for running the vehicle of the other of the front and rear pairs of left and right wheels; and a turn driving device for applying rotating torques in the rotating directions different from each other to the other pair of left and right wheels at the angular positions fixed by the rotating position fixing device to turn a vehicle body in a neighborhood of, that is, at or adjacent to the center point of the rotating axle for running the vehicle of the other pair of left and right wheels.
According to the four-wheel vehicle of the present invention described above, since one of front and rear pairs of left and right wheels, to which a running torque produced by the driving force is not transmitted, are supported for rotation concerning the respective axes perpendicular to the ground, and the one pair of left and right wheels are fixed during a vehicle body turning operation at the respective angular positions along the tangential directions of the arc passing the axes perpendicular to the ground of the one pair of left and right wheels, with the center of the arc located near the center point of the rotating axle for running the vehicle of the other pair of left and right wheels, it is possible to provide a relatively simple and small turning mechanism. In addition, since the radius of the arc passing the axes of the one pair of left and right wheels perpendicular to the ground and having the center near the center point of the rotating axle of the other pair of left and right wheels is the turning radius when the vehicle is turned, the turning radius is extremely small.
Further, since the other pair of left and right wheels are applied with rotating torques in rotating directions different from each other at the fixed angular positions of the one pair of left and right wheels, the vehicle body can be readily turned.
Also, since the turn driving device has a motor which drives either of two side gears for rotation while fixing a case for rotatably supporting the two side gears within a differential, it is possible to reliably turn the vehicle body in a neighborhood, that is, at or adjacent to the center point of the rotating axle of the other pair of left and right wheels.